the best one is the gun you shoot the best and break the most clay's with.i know how that sounds but everyone is different and different guns fit folks differently.so you need to shoulder as many kinds as you can to see what fits you the best,and hits where you point.
I can tell you what not to bring; A single shot. It was the only shotgun I had and while I did hit 10 of the 11 I shot at, my buddies had already taken down double that each. Reloading after every shot stinks.
As young 'uns, my brother and I used to shoot trap a lot with our dad. We each had Winchester youth model 20 ga. We shot damn near every weekend and got to the point where we could consistently hit doubles and had started on triples.
Really, what ever shotgun you have, if it's comfortable for you, is the right shotgun. It's the shooter that tracks, pulls the trigger and follows through, not the gun.
I use to shoot trap evey friday night. I'd see guys show up with $6500+ guns and go 39 for 50. I had a Beretta A-302 Trap Special that I got for $350 used and I carried a 46avg. Point is if you cant shoot trap, you cant shoot trap no matter how much the gun cost so dont think you need a high dollar gun just practice. There was one guy with an 870 that looked like he found it in the woods and if he went less than 49 for 50 he was having an "off day". I dont shoot as much trap as I use to but I can still dust um with my win 1300 just as good as the Beretta. I just feel it alittle more the next day with the 1300.